1. Technical Field
The present invention relates to angular rate sensors and electronic devices.
2. Related Art
Installation of acceleration sensors (accelerometers) on information equipment including digital cameras and hard disks and on automotive equipment including antilock brakes and air-bag systems has started. An acceleration sensor detects acceleration generated by vibrations and operations of equipment on which the acceleration sensor is mounted. As acceleration sensors, a strain-resistance type (see, for example, JP-A-2006-029992), and an electrostatic capacitance type (see, for example, JP-A-05-026902) have been proposed. Above all, vibration type acceleration sensors using oscillators are being extensively developed as they achieve higher sensitivity than other types.
However, crystal oscillators have been used in vibration type acceleration sensors in prior art. In the case of a tuning-fork shaped quartz oscillator, for obtaining a 32 kHz resonance frequency, the length of the prongs of the tuning fork becomes as large as several millimeters, whereby the entire length including the package becomes as large as almost 10 mm. Also, piezoelectric vibration devices that use a silicon substrate, instead of quartz, have been developed (see, for example, JP-A-2005-291858) in an attempt to achieve further size-reduction. When utilizing such piezoelectric vibration devices, since the thickness of a silicon substrate can only be reduced to about 100 μm, the prong length of the beams may become as much as several millimeters or greater in order to obtain a resonance frequency at several tens kHz. Therefore, further technological developments are necessary to reduce the size of the acceleration sensors.